In recent years, various aiding apparatuses have been developed for aiding the movements of the physically disabled or the elderly persons. For example, Patent Document 1 discloses a wearable motion assistive device that has a joint that mutually rotatably connects plural arms. An actuator rotates one arm relative to another, and a rotation angle of the arm is detected by an angle sensor.
In another example, Patent Document 2 discloses a rotation angle detecting apparatus in which a detection element is disposed in a radial direction of a rotating axle. In this rotation angle detecting apparatus, a reflective tape is spirally fixed on a circumferential surface of the rotating axle. Light is projected in a direction intersecting the reflective tape, and reflected light from the reflective tape is captured with the detection element. Based on the amount of displacement in the incident position of the reflected light from the reflective tape as the rotating axle is rotated, the rotation angle of the rotating axle is detected.
In another example, Patent Document 3 discloses a monitoring system for monitoring an operating status of a motor. In this monitoring system, plural sensors are used to monitor the operating status of the motor. If data regarding the operating status exceeds a threshold, an alert is displayed.    Patent Document 1: Japanese Laid-Open Patent Application No. 2005-95561    Patent Document 2: Japanese Laid-Open Patent Application No. 9-14941    Patent Document 3: Japanese Laid-Open Patent Application No. 2005-25751